What is the purpose of a neutral grounding resistor (NGR) in an impedance-grounded system?

• A. Limit fault current and provide a controlled path for ground fault protection.
• B. Increase fault current to ensure faster clearance.
• C. Insulate the neutral from earth completely.
• D. Arc suppression only during switching operations.

Answer: (A)

In an impedance-grounded system, the neutral is tied to earth through a resistor to limit the energy of a ground fault and to provide a predictable path for protection devices. The neutral-grounding resistor sets a controlled fault current when a line-to-ground fault occurs, so the current is enough to trip protection but not so high that equipment or insulation are severely damaged. This arrangement keeps the system energized on the remaining phases and reduces overvoltages, while allowing ground-fault relays to detect the fault and clear it quickly.

The option describing limiting fault current and providing a controlled path for ground-fault protection best captures this purpose. Increasing fault current would cause more damage and make protection harder to coordinate. Completely insulating the neutral from earth defeats the grounding scheme and the protective signaling. Arc suppression during switching is a separate consideration and not the primary role of the neutral grounding resistor.